The invention relates to a tool holder for use in machine tools, comprising a main body, which rotates about an axis of rotation, and cutter holders which each hold a cutting plate and can be radially adjusted by means of an axially displaceable control rod and coupling means.
Tool holders of this kind are used for turning work, in particular for producing an inner recess, hereinafter called a turned groove. In this connection, tool holders are known which have an axially displaceable control rod which can be driven in an axial movement by means of a machine-side hydraulic or electric servo drive. The axial movement is converted by suitable coupling means, for example via a wedge mechanism that can be actuated by the control rod, into a radial movement of a single cutter holder on which a cutting plate is disposed which comes into engagement with the workpiece to be machined. A tool holder of this kind is known from DE 40 22 579 A1, for example. The latter is for single-cutter machining.
Alternatively, tool holders are already known in which, for the purpose of producing a turned groove, a plurality of cutters are disposed about the circumference of a rotating mount which for its part revolves on a circular trajectory. In this kind of circular milling work, individual cutters successively engage the workpiece which is to be machined.
U.S. Pat. No. 4,275,624 discloses a tool holder in which two cutter holders are simultaneously provided which are disposed at an axial distance from one another and can be adjusted in the axial direction by means of an eccentrically mounted and axially displaceable control rod with an oblique toothing. A cutting tool can be fixed on each of the cutter holders, so that two turned grooves axially spaced apart from each other can be made simultaneously in a workpiece. For each turned groove, only one cutting tool comes into engagement with the workpiece.
Tool holders for single-cutter machining and tool holders with a plurality of cutters for circular machining have the disadvantage that the surface quality obtained with them in the turned groove, and the geometric roundness of the latter, is in many cases unsatisfactory, with the result that re-machining may be necessary. In addition, the turned groove requires a considerable production time.
It is an object of the present invention to form a tool holder of the type mentioned at the outset in such a way that it is possible, within a very short time, to produce a turned groove which satisfies stringent demands regarding surface quality and geometric roundness.
According to the invention, this object is achieved, in a tool holder of the generic type, by the fact that the tool holder has at least two cutter holders which can be radially adjusted between a retracted position and an extended position and whose cutters can be simultaneously brought into engagement with a workpiece in order to produce a turned groove. Using a plurality of cutter holders whose cutters simultaneously engage with the workpiece during machining provides for mutual supporting of the cutters. This results in a higher degree of precision and, consequently, a particularly high surface quality of the turned groove which is produced. Moreover, it is thereby possible to meet very stringent demands in respect of the geometric roundness of the turned groove. In addition, the simultaneous use of a plurality of cutters permits a considerable reduction in the time needed to produce the turned groove. This provides considerable cost advantages for the user, which in turn leads to savings on production units and represents a significant potential for rationalization.
The tool holder preferably comprises three cutter holders disposed about a circumference of a circle and each with an associated cutter. The use of three cutters effects particularly reliable mutual support, and by this means the radial feed can also be increased by a factor of 3 compared to machining of the workpiece with only one cutter, as a result of which, once again, the time needed to produce the turned groove can be correspondingly reduced. In this connection, provision can be made for the tool holders to be disposed uniformly about the circumference. A non-uniform distribution can be particularly advantageous since the non-uniform introduction of force which can thereby be obtained results in strong damping of vibrations.
The radial movement of the cutter holders is produced by the control rod, the movement of which is transmitted to the cutter holders via suitable coupling means. A hydraulic or electric servo drive can be used on the machine side for driving the control rod. However, it is particularly advantageous if the drive of the control rod is effected mechanically. For this purpose, provision can be made for the tool holder to comprise gear means for converting a rotation movement of the main body into an axially oriented reciprocating movement of the control rod. In such an embodiment, the main body has a dual function. On the one hand, the rotation movement guarantees a corresponding rotary movement of the cutters, and, on the other hand, the rotation movement of the main body serves as a drive for the control rod, which in turn produces the radial movement of the cutter holders. Such a configuration has the advantage that on the machine side only a drive spindle has to be provided to which the main body can be coupled in order to obtain a rotation movement, and so a hydraulic or electric servo drive on the machine side can be dispensed with. In this case, the tool holder has a purely mechanical drive system and can therefore be of particularly robust construction.
In order to be able to easily adapt the working stroke of the cutter holders, between their retracted position and their extended position, to the specific conditions of use, it is advantageous if the axial stroke of the control rod is adjustable. For this purpose, depending on the axial stroke which is desired, different gear means can be used for converting the rotation movement of the main body into the axial movement of the control rod.
In a preferred embodiment, the gear means comprise two cam elements which can rotate relative to one another and bear on one another via a control cam which is oriented obliquely with respect to the axial direction. The cam elements can be of annular construction, for example, and can enclose the main body about its circumference, it being ensured that they have a different speed of rotation relative to one another. At least one cam element forms a control cam on which the other cam element bears, and, as a result of the oblique orientation of the control cam, an axial movement is produced by the relative turning of the cam elements which bear on one another.
In this connection, it is advantageous if a first cam element is coupled to the main body via a toothed gearing. In this way, the rotation movement of the main body is transmitted to the first cam element via the toothed gearing.
The toothed gearing can be constructed in the manner of a planetary gear, for example, and can have two planetary wheels disposed on a common axis of rotation, connected rigidly to one another and each meshing with a toothed ring, the toothed rings preferably being oriented coaxially with respect to the axis of rotation of the main body and each surrounding said main body. In this connection, a first toothed ring can be mounted nonrotatably on the main body and thus executes a common rotation movement with the latter, while the second toothed ring has a different speed of rotation in relation to the main body. The first cam element is preferably mounted directly and in a rotationally fixed manner on the second toothed ring. By selecting the desired transmission ratios, on the one hand between the toothed rings and the planetary wheels, and, on the other hand, between the two planetary wheels, the speed of rotation of the second toothed ring and of the first cam element can thus be adjusted.
A rotation movement of the second cam element can be obtained by the fact that it is connected rigidly to the control rod, which control rod is mounted on the main body in such a way as to be axially displaceable but not rotatable. Because of the nonrotatable mount, the control rod has the same speed of rotation as the main body, with the result that the second cam element connected rigidly to the control rod also has the identical speed of rotation.
The reciprocating movement of the control rod is produced by means of the control cam. In this connection, it is of advantage if the return movement of the control rod is spring-assisted. Thus, for example, provision can be made for one of the two cam elements, for example the second cam element, to be spring-loaded in the direction of the other cam element. By this means it is possible to ensure that the two cam elements bear securely on one another even at very high speeds of rotation. The spring-loading can be produced, for example, by means of a compression spring, which bears on the control rod, and is transmitted from this to the second cam element connected to it.
The coupling means disposed between the control rod and the cutting plates have not yet been explained. In a preferred embodiment of the tool holder according to the invention, the cutter holders are mounted displaceably in radially oriented guides and each bear on a slide surface, of the control rod, oriented obliquely with respect to the axis of rotation. It is thus ensured, in a particularly simple way in terms of construction, that the cutter holders are displaced radially from their retracted position to their extended position when the control rod is moved axially forward.
In order to ensure a forced return of the cutter holders from their extended position to their retracted position upon a reverse axial movement of the control rod, an elastic return element is preferably provided. A particularly preferred embodiment in this connection is characterized in that the cutter holders comprise a carriage which is displaceable between the retracted position and the extended position and on which the cutter is mounted, and a return spring loading the carriage in the direction of its retracted position.
In order to ensure that the cutter holders do not execute any uncontrolled, radially outwardly directed movement as a result of the centrifugal forces induced by rotation, the cutter holders, in a particularly preferred embodiment, are mounted displaceably on the control rod and can be positively connected thereto. The positive connection ensures that the cutter holders bear securely on the control rod even at high speeds of rotation. An uncontrolled movement is avoided.
The positive connection can be configured, for example, as a dovetail guide. In a structurally particularly simple embodiment of the positive connection between cutter holder and control rod, a guide slot is provided on one of the parts to be connected, and a tension bolt of complementary configuration fixed on the other part engages in the guide slot.
It is advantageous if the tool holder comprises an adjustment mechanism for adjusting the setting of the cutter holders in their retracted position. In this way, the cutters mounted on the cutter holders and used for producing a turned groove can easily be adapted to the particular internal diameter of the workpiece bore which is to be provided with the turned groove.
In order to adjust or fine-tune the setting of the cutter holders, provision is preferably made for the length of the control rod to be able to be altered. The longer the control rod, the more the cutter holders bearing obliquely on it protrude radially outward. If the setting of the cutter holders is to be adapted, for example, to a smaller diameter of the workpiece bore, all that has to be done is to reduce the length of the control rod.
For this purpose, it is advantageous if the control rod has separate front and rear rod portions which can be connected to one another with adjustable axial spacing via an adjustment element.
The tool holder according to the invention comprises a plurality of cutter holders which each have a cutter and which, via mechanical transmission means, are driven in a radially oriented movement by the rotating main body, executing a radial movement from their retracted position to their extended position and back again to the retracted position. All the cutters come simultaneously into engagement with the workpiece and in so doing mutually support each other. To obtain a turned groove, all that has to be done is to drive the main body in a rotation movement so that the cutter holders extend outward for radial grooving and then resume their retracted position.
In a particularly preferred embodiment, the tool holder comprises a sensor unit for detecting the retracted position of the cutter holders. By means of the sensor unit it is possible to generate a stop signal for the machine-side drive of the main body, so that the machine-side drive of the main body can be switched off when the cutter holders have resumed their retracted position.
It is particularly advantageous if the retracted position and also the extended position of the cutter holders can be detected by means of the sensor unit. This permits particularly reliable monitoring of the grooving procedure.
The retracted position and advantageously also the extended position can preferably be detected in a contactless manner. In this way, mechanical wear of the sensor unit can be avoided.
In a preferred embodiment, the sensor unit has at least one Hall sensor, with which at least one corresponding magnet is associated. The retracted position of the cutter holders can thus be determined, for example, by means of a magnet being disposed on each of the cutter holders and having in each case a corresponding Hall sensor. Provision can also be made for contactless detection of the position of the control rod which corresponds to the position of the cutter holders since, because of the positive guidance of the cutter holders, there is an unambiguous relationship between the position of the control rod and the position of the cutter holders. Thus, for example, a plurality of magnets can be disposed on the second cam element connected rigidly to the control rod, the axial movement of the second cam element corresponding to the corresponding axial movement of the control rod.
It is advantageous if the tool holder has an electric voltage supply for the sensor unit, for example the Hall sensor, as it is thereby possible to dispense with an external electrical supply line.
The sensor signal made available by the sensor unit is evaluated and processed in a conventional manner by means of an electronics unit. The latter is preferably located adjacent to the sensor unit.
In an advantageous embodiment, the electronics unit can switch on and off automatically as a function of the rotation movement of the main body. It is thus possible to ensure that the electronics unit is switched on only when the main body is rotating and detection of the setting of the cutter holders is thus desired. Otherwise, the electronics unit is switched off, with the result that its power consumption is kept very low.
To allow the sensor electronics to switch on and off automatically, the tool holder can comprise, for example, a reed switch and an associated magnet.
The sensor unit is preferably associated with an electrical data transmission unit for wireless transmission of the determined position data to a machine-side control. In this case, the transmission can be, for example, by radio signal or infrared signal.
It is advantageous if the tool holder comprises a tool head which can be connected releasably to the main body and on which the cutter holders are disposed, and a stationary housing enclosing the main body. This makes it possible, in a particularly simple and time-saving manner, to exchange the desired cutter holders with fixed cutter while the entire tool head is detached from the main body.
The stationary housing preferably accommodates the sensor unit together with associated electronics and voltage supply, and the reed switch too can be mounted on the housing.